This invention relates to leveling devices to be attached to ladders for causing the ladder to adjust to and maintain a true vertical relationship rather than tilt laterally.
In 1959, Anderson and Studer were granted U.S. Pat. No. 2,894,670 for a ladder attachment to be mounted on a ladder by the purchaser, for self-leveling of the ladder. The attachment discloses the use of gear racks, gears, and gear locks, all in an extension at the bottom of the two ladder side rails or legs. Although this attachment device had advantages, it was, as admitted by Studer in his later U.S. Pat. No. 4,627,516, "relatively bulky and difficult for the average homeowner to install with sufficient confidence that the leveling attachment will work in the manner intended with the required safety." Furthermore, as explained by Studer, "the self-leveling attachment of my earlier invention required a considerable number of specially designed component parts which increased the weight and cost of the attachment, making it less attractive for purchase by the average home user desiring a self-leveling ladder." This prior '670 attachment of Studer and Anderson had to be assembled as it was mounted onto the ladder.
As a consequence of these problems, Studer developed a self-leveling mechanism formed as an actual part of the ladder, i.e., an integral ladder mechanism, so that, "the self-leveling mechanism is incorporated into the ladder at the factory," as set forth in the '516 patent. Because it was made at the factory, the buyer did not have to assemble/mount it on the ladder.
However, there are many thousands of ladders already owned by homeowners, repairmen, businesses, etc., which could beneficially use a ladder leveling attachment if it did not have the disadvantages of the previous attachment unit. Since such ladders are already manufactured, it is too late for a leveling attachment to be mounted at the factory. Moreover, many buyers of ladders do not realize they need a leveler until after a new ladder is purchased and used.